While having the muffler replaced on my 1991 300E, I mentioned to the mechanic that the car idles rough when at a stop with the car in gear and the AC on. If I turn off the AC it smoothes right out. No problem with acceleration or while cruising. He tested the ICV and said that there is no power going to it and that it may be a wire, harness, or pod issue and that it may cost from $100 to $1000 to diagnose and fix.

Does this sound right? Anything I can check before I sink $$ into it?
Idaes?

On that car...........the idle control valve is controlled by the CIS-E computer.

Not a 12V circuit.

You need a meter with duty cycle function to measure control circuit.
You can't disconnect to test! the connector must be slid back but not disconnected.
At that time you start car & measure duty cycle between the 2 pins, MUST be careful NOT to touch them together!!